1. Field of the Invention
The present invention relates in general to an improvement of slot type electrical terminals and more particularly to the electrical terminal blocks employing slot-type terminals.
2. Description of the Prior Art
Generally, terminal blocks employing electrical terminal contacts, are used in great variety and numbers in communication equipment to facilitate electrical connection of insulated electrical conductors to the contacts in the data processing system and harness thereof as well as to other conductors. In the past, the electrical connection has been accomplished by stripping the insulation from one end of the conductor and then soldering the conductor to the terminal contacts.
As a method of connecting an insulated conductor into a contact of a conductor terminal, there has been proposed soldering of the conductor material to the contact. However, this procedure requires considerable skill on the part of the workmen making the solder connection and is somewhat cumbersome and time consuming. In order to overcome these disadvantages, terminal blocks employing insulation-penetrating slot-type terminal contacts have been developed. The slot type terminal includes a pair of electrically conductive vertical blades, "each having a slot", or "forming slot theerhetween" at free ends thereof as a contact. The construction of blades permits electrical connection simply by penetrating the insulation of conductors. The penetration into the insulation is obtained by compressive forces applied to the conductors during seating of the wire in the terminal contact slot without stripping the insulation. In this slot-type terminal, problems may arise during the insertion procedure in that the crimping action of the slot to the conductor material requires that the conductor be restrained from flexing at this point so as not to damage the conductor. The flexing may cause degradation of the conductor material which ultimately results in its breaking off.
The conventional conductor connecting terminal will be described hereinbelow with reference to FIGS. 1 to 3.
FIG. 1 shows an exploded view of the conventional connector block provided with the slot type terminal block. W denotes the insulated conductor, reference number 1 denotes terminal block body, 2 denotes the conductor connecting terminal included in the terminal block body, and 3 denotes the cover thereof.
FIG. 2 shows the cross sectional view of the insulated conductor. Wc denotes insulated conductor, D denotes the diameter of the conductor material, and Wi denotes the insulation of the conductor.
FIG. 3 shows the perspective view of the conventional slot-type connecting terminal, finished with connection of the related insulated conductor, widely used in the terminal block shown in FIG. 1.
With reference to FIG. 1, a terminal block body 1 which allows connection of plurality of conductors has a plurality of recesses 4 for accepting related insulated conductor connecting terminals 2 in the shape of conductive strip material. As can be seen in FIG. 3, each of the connecting terminals 2 is comprised of an elongated rectangular base portion 5, a pin connector portion (not shown) extending at one end of said base portion, and a pair of upstanding blades 6 and 6, first blade 6 being extended upwardly at the other end of the base portion 5 and second blade 6 being extended upwardly and in parallel with said first blade at a distance therefrom. The upstanding blades 6 and 6 have respective U-shaped slots 8 in the vicinity of the center of the free end thereof provided with a pair of downwardly converging and oppositely disposed tapered edges 7 and 7. Said edges 7 and 7 form a pair of knife edges with sharp-edged blade therebetween. Since the distance between opposite knife edges substantially equals the diameter of the conductor Wc, depressing the insulated conductor into the slot 8 results in penetration of the knife portion into the insulation and thus the making of electrical connection of the insulated conductor with connecting terminals through both edges of the knife. In other words, electrical connection between the conductor material Wc of the insulated conductor W and connecting terminal 2 will be established at the two contact points C.sub.1 and C.sub.2. This electrical connection can be obtained with the aid of crimping action caused by the elastic restoring force of the blades at the slot 8, especially at said contact points C.sub.1 and C.sub.2 of the upstanding blades.
When insertion of the insulated conductor into the slot of the conductive conductor connecting terminal has been finished, a separate protective cover 3 is mounted. As shown in FIG. 1, said cover 3 is mounted onto the terminal block body by fitting the downward protrusion 9 and 9 at opposite ends of said cover into corresponding recesses 2' and 2' formed at opposite ends of the terminal block body 1 or with a plurality of screws at several points, i.e. four corners.
In this type of conventional slot-type terminal, electrical connection is made only at a pair of contact points between the pair of knife portions at both upright edges of the slot and the conductor material. The connection between the other portion of the conductor material and terminal at the crescent shaped portion R of the insulation may not be established, and thus, reliability of the connection will be degraded. Moreover, since the upstanding blades 6 and 6 crimp the related conductor material at said pair of contact points C.sub.1 and C.sub.2 only with elastic restoring force, force becomes concentrated at points C.sub.1 and C.sub.2. The conductor material will suffer extremely high stress and thus lead to bending of the conductor and to damaging or in the worst case, to breaking off of the conductor material. Otherwise, although immediate breaking off will not occur, occurrence and progression of the cracking at the contact point will lead to breaking off after a long period of use.
Also, in order to inspect any connection fault of the conductor from the conventional terminal block, the cover 3 should be removed. When the cover is removed, all conductors will be exposed at one time. Accordingly, careless treatment of the operator may cause electrical shorts and damage the related electrical equipment. Thus, careful treatment is required during inspection or maintenance. Thus, when opening or removing the cover, the power supply applied to all of the related electrical equipment except the equipment to be inspected should be turned off.
In order to simplify the manufacturing process of the terminal block, connecting terminal made of a conductive strip and having inverted U-shaped perpendicular portion at one end of the conductive strip has been proposed. Said perpendicular portion is formed with a slot.
As described hereinbefore, the conventional terminal block has the disadvantage of requiring careful handling and may cause breaking off of the conductor materials.